Load commutated inverters (LCI) are widely used in the process industry for the high power variable speed motor range. It offers a simple and reliable design where a minimum number of sensors are required. A simplistic view of a typical setup is illustrated in FIG. 1. Grid side voltage transformers 4 are used for synchronizing firing angle control to grid voltage. Grid side current transformers 1 are used to estimate a dc-current, which again is used for current control of grid side converter. Motor voltage transformers 2 are used for measuring motor voltage, which is necessary for detecting motor rotor position as well as for motor voltage control.